Method of forming anodic titanium oxide layers having dual-color appearance and article having the same

ABSTRACT

A method of forming anodic titanium oxide layers having dual-color appearance includes the following steps: providing a cleaned substrate; depositing a titanium film on the substrate; forming a mask of a desired pattern covering a portion of the substrate; carrying out a first anodization by immersing the substrate in an electrolytic solution as anode; applying a first direct-current voltage to produce a first titanium oxide layer; removing the mask; carrying out a second anodization by immersing the substrate in the electrolytic solution as anode; applying a second direct-current voltage having a value smaller than that of the first voltage to produce a second titanium oxide layer; and cleaning the coated substrate. The instant disclosure also includes an article made by the above method.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The instant disclosure relates to a method of forming anodic titaniumoxide layers having dual-color appearance and an article having thesame; more particularly, to a method of forming titanium oxide layers ona substrate, such that the substrate would have at least two differentcolor finishes, and an article having the same.

2. Description of Related Art

Portable electronic devices are very popular today, such as mobilephones, personal digital assistants (PDAs), laptops, etc. As theconsumers begin to put more focus on the cosmetic appearances of theseportable electronics, the housings of most portable electronics haveshiny finishes for attractiveness. Especially for metal surfaces, whichtypically are specially processed to attain smoothness and shininess forvisual attractiveness.

To apply color on surfaces of a housing, the existing technique involvesanodizing to form a thin layer of titanium oxide on the metal surfacefor coloring. However, coloration done by such technique restricts themetal surfaces to a mono-colored state, unable to generate multi-colorvariations. Furthermore, the titanium oxide layer of differentthicknesses formed by anodizing generates different colors, while itsthickness depends on factors such as applied voltage. However, inpractice, the process of forming multiple titanium oxide layers on asame housing to create different colorations thereon is quitechallenging.

To form a different color on the housing, an alternative solution is toapply a plastic adhesive film to its metal surface. However, since theadhesive film covers the metal housing, the user is unable to sense theactual metallic color and touch feel.

Therefore, the challenge of producing at least two different colors on ametallic housing while maintaining the metallic touch feel is a mainissue the manufacturers intend to resolve.

SUMMARY OF THE INVENTION

To address the aforementioned issues, the instant disclosure provides amethod of forming anodic titanium oxide layers having dual-colorappearance and an article having the same. The main objective is toresolve the issue of forming at least two metallic colors on asubstrate, especially by anodizing, while maintaining metallic lusterand its touch feel.

The method comprises the following steps: providing a substrate;cleaning the substrate; depositing a titanium film on the substrate;forming a mask of desired pattern over a portion of the substrate;taking the substrate having titanium film formed thereon as an anode andimmersing into an electrolytic solution; applying a first direct-currentvoltage through the electrolytic solution to oxidize the surface of thetitanium film and produce a first titanium oxide layer on the substrate;removing the mask; taking the substrate as an anode and immersing itagain in the electrolytic solution; applying a second direct-currentvoltage having a smaller value than that of the first-direct voltagethrough the electrolytic solution, to oxidize the surface of thetitanium film and produce a second titanium oxide layer on thesubstrate; and cleaning the substrate.

The instant disclosure also provides an article having anodic titaniumoxide layers with dual-color appearance obtained by the above method.The product comprises a substrate and a titanium film formed thereon.The surface of the titanium film is oxidized in forming a first titaniumoxide layer and a second titanium oxide layer thereon in anon-overlapping manner. The first titanium oxide layer shows a firstcolor, while the second titanium oxide layer shows a second color.

For advantages, by first passing a high-voltage direct current foranodizing in forming the first titanium oxide layer having the firstcolor, followed by passing a low-voltage direct current for anodizing informing the second titanium oxide layer having the second color, themetal housing can be easily color-coated and maintain its metallicluster. The method does not produce dust contaminants and surfacedamages as would with sand blasting, nor requires adhesive film. For theabove method, the process time is short, which is suitable for massproduction. For example, each oxidation process only takes approximatelyone minute, while a particular color is being introduced on the surfaceof the housing. The color-forming oxidation process can be repeated withgreat accuracy by controlling the factors such as electroplating time,electrolytic solution, and voltage.

In order to further appreciate the characteristics and technicalcontents of the instant disclosure, references are hereunder made to thedetailed descriptions and appended drawings in connection with theinstant disclosure. However, the appended drawings are merely shown forexemplary purposes, rather than being used to restrict the scope of theinstant disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a step-by-step illustration of forming anodic titanium oxidelayers having dual-color appearance of the instant disclosure.

FIG. 2 is a flowchart showing the steps of a preparation process A ofthe instant disclosure.

FIG. 3 is a flowchart showing the steps of a first anodizing B1 of theinstant disclosure.

FIG. 4 is a flowchart showing the steps of a second anodizing B2 of theinstant disclosure.

FIG. 5 is a perspective view showing the use of instant disclosure for ahousing of the electronic device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Please refer to FIG. 1, which shows a step-by-step illustration of themethod in forming anodic titanium oxide layers having dual-colorappearance of the instant disclosure. The present method can be brokeninto a preparation process A, a first anodizing B1, removal of the maskA2, and a second anodizing B2. Each different stage is explained indetails hereinbelow.

[Preparation Process A]

Please refer to FIGS. 1 and 2, with FIG. 2 showing a flowchart listingthe steps of the preparation process A of the instant disclosure. Instep A11, a substrate 102 is provided. The substrate 102 is mainly madeof metallic material and can be a metal housing, such as aluminum,aluminum alloy, stainless steel, or magnesium alloy housing. Thesubstrate 102 may also be a non-metallic housing as well.

Then, for step A12 regarding the metal housing, the substrate 102 mayfirst be cleaned prior to anodic treatment. Generally speaking, thecleaning process includes degreasing, acid washing (pickling), rinsing(water), and drying. Degreasing is performed to remove oil and greaseoff the surface of the substrate 102, which can be done by immersing thesubstrate 102 in a solvent bath. Acid washing, or pickling, is used toremove rust or oxidation layer from metal surfaces. Different pickleliquors, which contain strong acids, are used for different metals. Forexample, common steel can be treated with hydrochloric acid or sulfuricacid. If necessary, a corrosion inhibitor can be added to decrease thecorrosion rate of the metal. For stainless steel, mixed acid of nitricacid and hydrofluoric acid is used. Low concentrations of nitric acidcan be used to treat aluminum and its alloy. Rinsing is then performedto remove any debris left on the surface of the substrate 102 after acidwashing, followed by drying the substrate 102 itself.

Next, in step A13, a titanium film 104 is deposited on the substrate102. The deposition technique may be physical vapor deposition (PVD),such as vacuum sputtering or evaporative deposition. The thickness ofthe titanium film may be 0.5 to 1.5 micrometers. The aforementionedcoating technique can be used for substrate made of different metallicmaterial or even for non-metallic substrate.

Then, in step A14, a mask 106 of desired pattern is formed on thesubstrate 102. The masked portion of the substrate 102 is reserved forsecond anodizing, while the first anodizing B1 is being conducted. Thepreparation process A has thus been completed up to this point, beforeadvancing to the process of applying first coloration through anodizing.

The aforementioned mask 106 can be a tape, preferably a peelable mask.The peelable mask has a low cost, is easy to use, and does not leave anymark behind. Using the peelable mask, the mask 106 can be formed on thesubstrate 102 by the screen printing technique in a particular pattern.Often used to protect certain parts of a printed circuit board, thepeelable mask is a strippable coating formed by a dried liquid-basedprotective ink after being transferred onto the substrate 102.

[First Anodizing B1]

Please refer to FIGS. 1 and 3, with FIG. 3 being a flowchart showing thesteps of the first anodizing B1. For a first step B11, the substrate 102having the titanium film 104 thereon is immersed in an electrolyticsolution and serves as an anode. For the instant disclosure, theelectrolytic solution must be acidic, such as sulfuric acid, sodiumphosphate, chromic acid, etc. For example, a sample electrolyticsolution can include sulfuric acid in an amount between approximately0.1% and 10% by volume. The preceding example is only for explainingpurpose. Since different electrolytic solutions differ chemically, theoxide coatings to be grown would have different characteristics as well.For example, the oxide coating obtained through the sulfuric acidsolution has excellent corrosion and wear resistances.

Next, for step B12, a first direct-current voltage is applied throughthe solution to oxidize the surface of the titanium film 104. The valueof the first direct-current voltage is greater than a seconddirect-current voltage to be applied later in the second anodizing B2.Preferably, the first direct-current voltage is above 30 volts tooxidize the surface of the titanium film 104, where the first directcurrent may be a constant current. After a short period, approximatelyone minute, as shown in step B13, a first titanium oxide layer 104′ isformed on the substrate 102. If the voltage is high enough, thethickness of the first titanium oxide layer 104′ can be increased to top300 nanometers. Thereby, the surface hardness of the titanium coatingcan be increased against wear, such as for a housing of the electronicdevice. Through the formation of the first titanium oxide layer 104′, afirst color is applied on the substrate 102. The color is produced bythe reflection of light at and through the formed oxide layer, which istransparent and electrically insulated. More specifically, the color isproduced by the interference of first reflected light wave from theupper surface of the titanium oxide layer with the second reflectedlight wave from the lower surface of the titanium oxide layer, where theinteraction of light waves produces the phenomenon called interferencecoloring. Oxide layers having different thicknesses can producedifferent light interferences of various colors. Notably, the nanoporesformed on the titanium oxide due to the acid in the electrolyticsolution do not require sealing.

Next, the substrate 102 is removed from the electrolytic solution. Ifnecessary, the substrate 102 can be cleaned with water and dried. Thedrying process is conducive in removing the peelable mask. Then, themask removal process A2 is proceeded to remove the mask 106 for exposingportion of the substrate 102 not oxidized. The substrate 102 is nowready to undergo the second anodizing B2 in forming a second color.

[Second Anodizing B2]

Please refer to FIG. 4, which is a flowchart showing the steps of secondanodizing of the instant disclosure, in conjunction with FIG. 1. In stepB21, the substrate 102 having a first color is again immersed in theelectrolytic solution and serves as an anode. The electrolytic solutionused during the first anodizing B1 may be used again for the presentstep. Next, for step B22, the second direct-current voltage having asmaller value than that of the first direct-current voltage is appliedthrough the electrolytic solution to oxidize the surface of the titaniumfilm 104. For example, the first direct-current voltage may be 35 volts,and the second direct-current voltage can be 15 volts. The recommendedminimum difference is in the 2- to 5-volt range. After a period of time,approximately one minute, as indicated by step B23, a second titaniumoxide layer 104″ is formed on the substrate 102. Visually, the formationof the second titanium oxide layer 104″ by the second direct-currentvoltage does not cause any significant negative impact on the cosmeticeffect of the earlier formed first titanium oxide layer 104′. In otherwords, the first color formed by the first titanium oxide layer 104′ isnot affected by the second color formed by the second titanium oxidelayer 104″.

During anodizing, if the composition and concentration of theelectrolytic solution changes within a tolerated range, only the sizesof the nanopores would be affected, while the thicknesses and colors ofthe oxide layers remain basically unaffected. The overriding factor indetermining the thicknesses of the oxide layers is current density,which is typically voltage-controlled. As voltage increases, a thickercoating is produced. Combines with the light interference effect aspreviously mentioned, the change in coating thickness produces differentcoloration on the substrate 102.

The instant disclosure also discovered that if lower voltage is appliedbefore higher voltage for anodizing, the produced oxide layers andcolorations are unstable. Conversely, if the surface of the substratefirst undergoes high voltage process in the first anodizing and followedby low voltage process in the second anodizing, the earlier formed oxidelayer by the high voltage process can remain stable with minimal colorchange over time.

To illustrate the above argument, an example is given hereinbelow. Thefirst direct-current voltage is 35 volts, and the second direct-currentvoltage is 15 volts, with sulfuric acid being the electrolytic solution.The measured lab values based on the CIE (Int'l Commission onIllumination) are as follows:

[After the First Anodizing]

The lab values of the first color are: 75.25, −9.72, −7.03

[After the Second Anodizing]

The lab values of the first color are: 72.01, −9.43, −4.34

The lab values of the second color are: 26.23, 26.75, 12.98

The above lab results show the first color is not significantly affectedafter the second anodizing. However, if the setting is reversed, suchthat the first direct-current voltage for the first anodizing is 15volts and the second direct-current voltage for the second anodizing is35 volts, the corresponding lab results show the first color issignificantly affected by the second anodizing where the first colorsuffers significant change.

Lastly, the substrate 102 is thoroughly cleaned. The cleaning step caninclude water rinsing and drying, where the drying temperature may beapproximately in the 120- to 150-° C. range.

Based on the above method of the instant disclosure, an article havinganodic titanium oxide layers with dual-color appearance can befabricated. Moreover, by using the peelable mask and the screen printingtechnique, different cosmetic designs can be formed on the metalsubstrate, such as letters, decorative patterns, etc. As shown in FIG.5, a housing 100 of an electronic device is illustrated. The first colorof the first titanium oxide layer 104′ on the substrate 102 serves asthe background color. A decorative pattern made up by the letters “A”,“B”, and “C”, which is created by the peelable mask, is shown by thesecond color of the second titanium oxide layer 104″ without affectingthe first color.

Based on the method of forming anodic titanium oxide layers havingdual-color appearance and the article having the same of the instantdisclosure, the associated advantages and attributes are as follows. Byusing the deposition technique to deposit the titanium film, such asvacuum sputtering for the housing of the electronic device, up tothousands of housings can be processed simultaneously, with titaniumcoating being more cost-effective than using pure titanium substrate.Furthermore, by first forming the first titanium oxide layer having thefirst color through high-voltage anodizing, followed by forming thesecond titanium oxide layer having the second color through low-voltageanodizing, the metal housing can be easily processed to display itscolorations with metallic touch feel. Moreover, the second titaniumoxide layer formed by the low-voltage anodizing would not induce anynegative impact on the color of the first titanium oxide layer formedearlier in the process.

Other attributes of the instant disclosure include short fabricationtime, which is suitable for mass production. Special colorations can beformed on the surfaces of the housing. By adjusting the electroplatingtime, the electrolytic solution, and voltage, the colorization of thesubstrate can be accurately controlled with excellent repeatability. Theyield rate can be improved significantly.

The descriptions illustrated supra set forth simply the preferredembodiment of the instant disclosure; however, the characteristics ofthe instant disclosure are by no means restricted thereto. All changes,alternations, or modifications conveniently considered by those skilledin the art are deemed to be encompassed within the scope of the instantdisclosure delineated by the following claims.

What is claimed is:
 1. A method of forming anodic titanium oxide layershaving dual-color appearance, comprising the steps of: a. providing asubstrate; b. cleaning the substrate; c. depositing a titanium film onthe substrate; d. forming a mask of desired pattern over a portion ofthe substrate; e. carrying out a first anodization process by immersingthe substrate in an electrolytic solution as an anode; f. applying afirst direct-current voltage through the electrolytic solution toproduce a first titanium oxide layer on the substrate; g. removing themask; h. carrying out a second anodization process by immersing thesubstrate in the electrolytic solution as an anode; i. applying a seconddirect-current voltage having a value smaller than that of the firstvoltage to produce a second titanium oxide layer on the substrate; andj. cleaning the substrate.
 2. The method of forming anodic titaniumoxide layers having dual-color appearance of claim 1, wherein thesubstrate is a metallic housing.
 3. The method of forming anodictitanium oxide layers having dual-color appearance of claim 1, whereinthe thickness of the titanium film is in the range of 0.5 to 1.5micrometers.
 4. The method of forming anodic titanium oxide layershaving dual-color appearance of claim 1, wherein the cleaning stepbefore depositing the titanium film includes degreasing, acid washing(pickling), rinsing (water), and drying in sequence.
 5. The method offorming anodic titanium oxide layers having dual-color appearance ofclaim 1, wherein the voltage of the first direct current is at least 30volts.
 6. The method of forming anodic titanium oxide layers havingdual-color appearance of claim 1, wherein the difference between thevoltages of the first direct current and the second direct current is atleast 2 volts.
 7. The method of forming anodic titanium oxide layershaving dual-color appearance of claim 1, wherein the mask may be apeelable mask formed on the substrate by the screen printing technique.8. An article having titanium oxide layers with dual-color appearance,fabricated by the method of forming anodic titanium oxide layers havingdual-color appearance of claim 1, comprising: a substrate; and atitanium film formed on the surface of the substrate, wherein thesurface of the titanium film includes a first titanium oxide layerregion showing a first color and a second titanium oxide layer regionshowing a second color, the second titanium oxide layer region beingformed on a masked area.
 9. The article having titanium oxide layerswith dual-color appearance of claim 8, wherein the substrate is ametallic housing.
 10. The article having titanium oxide layers withdual-color appearance of claim 8, wherein the thickness of the titaniumfilm is in the range of 0.5 to 1.5 micrometers.
 11. The article havingtitanium oxide layers with dual-color appearance of claim 8, wherein thethickness of the first titanium oxide layer is greater than 300nanometers.